This invention relates to an improved method for the refining of hydrocarbon oils. More specifically, this invention relates to an improved pretreatment method for the reclaiming of used lubricating oils by the removal of solid and liquid impurities contained therein.
Critical shortages of petroleum have focused attention on ways and means of conserving dwindling supplies of crude oil and petroleum products until science and technology can close the gap with stimulated production, alternative energy sources and more efficient energy utilization. One approach to this problem has been to encourage better utilization of present supplies, which includes an estimated 1 billion gallons of used lubricating oil that is drained, dumped or burned each year in this country. These oils have generally been used as engine crankcase lubricants, transmission and gear oils and the like. These oils commonly contain various detergents and extreme pressure additives such as polyvalent metal soaps as well as impurities which result from oxidation of the oil itself, water and gasoline. Much of this oil could be reused if collected and effectively reprocessed. Instead, as much as one-third of it is indiscriminately dumped, contaminating both water and land. Some is burned and this, too, contributes to pollution of our environment by releasing metallic oxides into the atmosphere. These metallic contaminants originate, for the most part, from lubricant and fuel additives necessary for satisfactory engine performance.
Many processes are available for the purification and reprocessing of lubricating oils. Often these processes involve the use of distillation followed by polishing or decolorizing treatment. However, to prevent coking and column fouling during distillation, some form of pretreatment to remove many of the additives and contaminants from the oil is preferred. Some of these treatments are severe, oftentimes altering the petroleum base composition of the lubricating oil and resulting in the loss of a substantial quantity of otherwise recoverable organic material and ultimately producing a product deficient in properties required in high-quality lubricants.
Typically, the used oil is heated to drive off volatile hydrocarbons and water and to permit some of the solids to settle before adding a strong mineral acid which precipitates out a large portion of the oil as sludge. The supernatant oil is separated from the sludge, neutralized with a caustic and distilled or further treated with clay and filtered.
Other processes may utilize a caustic such as sodium hydroxide rather than an acid, but in either process a large percentage of the used oil is lost (up to about 50%) and large quantities of an acidic or caustic sludge remain which are increasingly difficult to dispose of due to environmental considerations. Additionally, severe treatments of the acid or caustic type result in a substantial loss of diaromatic and polyaromatic-polar materials from the oil which may approach 70% on an original oil basis. These higher molecular weight aromatics are generally associated with natural lubricity characteristics of the base oil and removal of these compounds would affect this parameter of the lubricant product. Likewise, the polar materials are responsible in part for natural resistance to oxidation, and selective removal of these compounds will contribute to poor oxidation stability of reprocessed lubricating oils. Both of these conditions can be overcome, to some extent, by the use of additives.
Still other treatment processes have been developed in an attempt to meet the environmental objections of the previous processes, by utilizing various hydrocarbon liquid diluents which may be also combined with solvents such as alcohol or water-alcohol mixtures to form solvent precipitation mixtures. While these processes do not result in a loss of the desirable aromatic compounds, neither do most of these solvent processes remove sufficient contaminants from the waste oil and so must be combined with additional steps which utilize an acid or other more severe treatment.
However, none of these processes appears to be able to remove only the undesirable used and unused additives and other solid and liquid contaminants from the used lubricating oil while leaving unchanged the desirable lubricity and anti-oxidant properties of the petroleum base.